1. Technical Field
The present invention relates to an organic-inorganic composite anion exchange membrane for non-aqueous redox flow batteries, which contains a polyvinylidene fluoride polymer, and a method for preparing the same.
2. Description of the Related Art
As energy consumption based on fossil fuels increases worldwide, it has become an essential task to secure sustainable energy sources such as sunlight, wind power, tidal power, biomass, and the like in order to replace fossil fuels. To this end, many efforts have been actively made to develop a technology for producing and storing new forms of renewable energy. Thereamong, redox flow batteries have drawn considerable attention as environment-friendly medium or large energy storage devices.
A redox flow battery refers to a device that stores electrical energy as chemical energy through oxidation and reduction of active materials dissolved in electrolytes, wherein charged each electrolyte separated by a membrane are stored in an external negative electrolyte reservoir and a positive electrolyte reservoir, respectively. Specifically, the redox flow battery has an advantage in that its energy storage capacity can be reduced or enlarged through size adjustment of two external electrolyte reservoirs that store active materials.
According to solvent type, redox flow batteries can be broadly classified into aqueous redox flow batteries using water and non-aqueous redox flow batteries using an organic solvent. Studies have been mostly focused on the aqueous redox flow batteries.
An ion exchange membrane of the non-aqueous redox flow battery has a great influence on durability. In order to transfer charge carriers upon charging and discharging and to separate a positive electrolyte and a negative electrolyte, selection of an ion exchange membrane is crucial. The non-aqueous redox flow battery has drawbacks in that different redox pairs of positive and negative electrodes can be mixed with each other and cause mixed contamination of the electrolytes, thereby causing self-discharge.
In order to resolve such problems, ion exchange membranes having high ion selectivity must be used. However, since there is no satisfactory ion exchange membrane in the art, there is a need for development of a novel ion exchange membrane for non-aqueous redox flow batteries.
A polyvinylidene fluoride polymer is known as having high chemical and physical resistance, and has been employed in medical analysis systems, water treatment systems, and energy systems. Although there are some cases where a cation exchange membrane is prepared from the polyvinylidene fluoride polymer and applied to an aqueous redox flow battery system in order to enhance performance of the aqueous redox flow battery system, no case has been reported where the polyvinylidene fluoride polymer is applied to a non-aqueous redox flow system.